High-frequency dielectric furnace



c. T. ALLQUTT HIGH FREQUENCY .nmnnc'rme FURNACE Filed Oct. 27. 1 923WITNESSES: INVENTOR 2 4 7 Chas fer T A//cuf7.

, ATTORNEY Patented Sept. 2 9, 192 5.

UNITED sTm'Es PATENT onl -cs.

CHESTER 'r. ALLCUTT, or rrrrsnvaen, rENNsYLvANrA, ASSIGNOR TO WESTING-HOUSE ELECTRIC. & MANUFACT RING COMPANY, A conroRATIoN or PENNSYL-vANIA.

HIGH-FREQUENCY DIELECTRIC FURNACE.

Application filed October 2 7, 1928.- Serial No. 671,113.

To all whom it may concern:

Be it known that I, CHESTER T. ALLCUI'I, a citizen of the United States,and a resident of Pittsburgh, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement in Hi h-Fre-'(f uency Dielectric Furnaces, of which the ollowing is a specification.

-My invention relates to electric heating and particularly to heating-bymeans of a high-frequency electric fleld.

The object of my invention is to provide a system of, and means for,heating by the use of a high-frequency electric field.

In practicing my invention, I provide a source of high-frequencyelectric current and connect the terminals thereof to two electrodesbetween which is located a member oi imperfect dielectric material whichbecomes heated when subjected to the high-- frequency electric fieldproduced between the electrodes. 1

In the single sheet of drawings, Figure 1 1s a schematic view of a highfrequency source of electric ener y operatively associated with afurnace, i lustrated in section, embodying my invention,

Fig. 2 is a schematic view of a modified form of high-frequency systemembodying my IIIVGIltiOIl,

Fig.3 is a View, in section, of a. further modification of a devicecomprising a part of a system embodying my invention,

Fig. 4 is a view, in section, of another modification of a deviceembodying my invention, 1 1 I Fig. Sis a schematic view of a stillfurther modification of a high-frequency heating system, and

Fig. 6 is a schematic view, in side elevation, of a commercialapplication of high frequency dielectric heating.

Referring more particularly to Fig. 1' of the drawin a source ofalternating current is here indicated by the conductors 11 that areconnected to the terminals of the primary winding 12 of a suitabletransformer.

The secondary winding 13 is connected t6 the terminals of a condenser14', of suitable type, and the connections empldyed are such as toprovide. a source, of sustained electric current of high frequency andof high voltage delivered to the conductors 15 and 16. A crucible 17 ofany suitable or convenient form has located thereon an enclosing theconductor 16. A mass 19, of a material to be heated, is located withinthe crucible 17 and is electrically connected to the con ductor 15.

The crucible 17 is made of a material that is an imperfect dielectricand which, when subjected to the action of the high-voltage alternatingelectric field existing between the mass of material 19 and the outerelectrode .18 when the system is energized, is heated by the loss ofenergy in the dielectric material itself. As is well known, the energyloss in a member of imperfect dielectric material when subjected toanfialternating electric field is dependent upon the geometricaldimensions of the member,-the material of which it is made, thefrequency ofthe field and the squareof the applied voltage.

In general, this loss is relatively small for such members where thedimensions of the crucible are relatively limited and it is,

- therefore, advisable tolemploy a frequency that is ashigh as iscommercially possible and a voltage that is as high as is practicable.

The crucible 17 may, for instance, be made of clay, porcelain or glassthat will be heated Whensubjectedto the action of a high frequency andhigh-voltage electric field and that will, at the same time, serve as acontainer for materials to be heated therein, the heat being generateddirectly in the crucible of dielectric materialand imparted to thematerial located therein by conduction.

Dielectric materials of the ordinary kind that may be employedascontainers are usually relatively poor conductors of electricitywhencool but become much better conductors when heated, that is, they have arelatively high negative temperature coefficient of resistivity. It isadvisable, therefore, to provide some means for counteractingthiseffect, which would result in a tendency of the current flowing througha member of dielectric material to concentrate at any point that. had arelatively high loss, such as mightbe caused by a defect in themateriaL- Such means may be provided by a condenser or by an air gapplaced in series relationtto the imperfectdielectric and such means isillustrated more particularly in Fig. 2 of the drawing, where thecrucible 17 has an electrode 21 surrounding it but spaced therefrom.This construction, of

course, reduces the inherent capacity of the structure, but provides.means for insuring that the current traversing the-member of imperfectdielectric material shall be substantially uniform over substantiallyits entire surface since the air between the members 17 and 21 is arelatively perfect dielectrio and there will be no tendency for thecurrent to concentrate at certainpoints.

The same effect may be obtained byemploying a member of relativelyperfect solid, die ectric material between the crucible and the outerelectrode. This is illustrated more particularly .in Fig. 3 of thedrawing, wherein the crucible 22 for containin the mass of materialLtobe heated is ma e of glass and is surrounded by a crucible 17, ofquartz, an electrode 18 being fitted closely around a portion-of theperi heral surface of the quartz crucible 3L7. s quartz is a much betterdielectric than glass, it will operate to prevent what may be termedlocal hot s ots in the crucible 22 and insure substantially uniformdistribution of current traversing the member 22.

The crucible 17 of quartz, illustrated in' Fig. -3 of the drawing, willalso be heated when sub'ected to the action of a high voltage andighfrequency electric field and will therefore assist in increasing thetemperature of the mass of material located within the inner crucible22.

A structure that may be used in heating non-conducting materials isillustrated in Fig. 4. A conducting electrode 23 is inserted in crucible24 of dielectric material, but is spaced therefrom by a mass of mate,-rial 25 to be heated. A second conducting electrode 26 surrounds thecrucible but is spaced therefrom as in the structure shown in. Fig. 2.When a source-13, of high-freuenc electromotive force, is connected to Qt e e ectrodes 23 and 26, the losses in the sir dtemps mass 25 ofnon-conducting material to be heated, supplemented by such losses as mayoccur in t the material in the crucible to attain the derature.

In Fig. 5, I have illustrated a relatively narrow. and elongatedcrucible or container 27 of a suitable imperfect dielectric mateor thesource of high and high voltage currentfhere illustrated u are ofrelativ thereby increasin crucible27. larly adapted for use in case thematerialrial. Electrodes 28 and 29 connected-to the frequency as a'seconds coil 13Qof. a transformer,

large surface area and ma be located a re tivel short distances acapacitance o the device and, there one, the power loss in the Thismodification is particucontained .in the crucible is non-conductiinlg InFig. 6, I have'illustrated schematic y one form in which the systemembodying my invention may be employed 0 mediately incorporated in t edielectric crucible 24, will cause cially. A sheet or strip 31, of highgrade' moisture and when subjected'to the action of a high-frequencelectric field is heated and any moisture t at may be in the paper willbe driven out thereby and the aper will, therefore, be thoroughly dry,i?

e condenser and suitably protected against reabsorption of moisture.This method is particularly advantageous because of the fact that thelosses and consequent heating of the paper are more or less restrictedto such of the paper as contain undesirab e moisture. Portions 'of thepaper that do not contain an undesirable quantity of moisture will haverelatively low dielectric losses'and will be but slightly heated.Obviously, a saving in power will result. Furthermore,

this method permits ofIvery rapid drying without danger of overheatingsince the losses diminish as the paper dries and overheating is therebyautomatically prevented. Where I have referred to a source of sustainedelectric current of high-frequenc I include fre uencies not less than tose usually emp oyed in radio telegraphy and radio telephony andsuchhigher frequencies as may be commercially roduced for suchapplications. A sustaine alternatin current of high frequency isparticular aplicable for my purpose, as the disc arge rom'a series 0high-frequency wave trains, such as produced by an oscillatory arkdischarge, will not produce the desired eatin efl'ects.

ortions I arious modifications and changes may be i made herein withoutdeparting from the s irit and scope of the invention, and I desire,therefore, that only such limitations shall placed thereon as are b theprior art or are specifically set forth in the a pended claims.

I c aim as my invention: j 1. In combination, a pair of terminal-members, a memberof imperfect dielectric material therebetween, and asource'ofhighfrequency current supply connected t id terminal mem rs.

. v l C 2. In a heatingsystem,a container of im- -perfect dielectricmaterial, and means for subiecting said. container to the action I of abig frequency current.

3. In an electric furnace, in combination,-

5. In an electric furnace, in combination,

a dielectric member and a source of highfrequency electromotive forcehaving its'terminals electrically connected to opposite sides of saiddielectric member.

6. In combination, a member of im rfect dielectric material, a pair oftermina mem-' bers, a source of high-frequency current supply connectedto said terminal members, and means for insuring a substantially uniformenergy loss throughout the mass of said dielectric member.

7.. In combination, a member ofimperfect dielectric material, a pair ofterminal members, a, source of high-frequency current supply connectedto sald terminal members, and means for insuring a substantially uniformcurrent density throughout the mass of said dielectric member under allconditions of operation. 7

8. In combination, a member of imperfect dielectric material, a sourceof high-frequency current supply, a pair of terminal members connectedto said terminals, operatively associated with said member of dielectricmaterial, and means havin a higher dielectric strength than said firstnamed dielectric material interposed between said terminal members andsaid member of imperfect dielectric material."

9. The method of heating a mass of material which com rises subjecting amember of imperfect die ectric material to a highfrequency electricfield and causing the heat I generated therein to heat said mass ofmaterial.

10. The method ofheating 21 mass of material located in .a container ofimperfect ing the container to the action of a highfrequency electricfield.

11. The method otheating a mass of ma terial located in a container ofimperfect dielectric material which comprises connecting one terminal ofa high-frequency circuit to said mass of material, connecting the otherterminal of said circuit to a terminal member located outside of saidcontainer, and energizing said circuit.

In testimony whereof,-I have hereunto subscribed my name this 22nd dayof October, 1923.

CHESTER T. ALLCUT'I dielectric material which comprises subject-,

